1. Field of the Invention
The present invention generally relates to a liquid crystal display apparatus and, more particularly, to a liquid crystal display apparatus of simple matrix type for simultaneously driving a plurality of scanning electrodes.
2. Description of Related Art
Generally, in the field of liquid crystal display apparatuses of simple matrix type, a liquid crystal display apparatus of dual scan type is known in which a liquid crystal panel screen is divided into an upper half screen and a lower half screen and a segment driver and a common driver are provided for each of these screens to drive the same independently of each other.
However, the above-mentioned dual-scan liquid crystal display apparatus requires to provide the segment driver and the common driver for each of the screens, thereby pushing up the fabrication cost.
To lower the cost, a technique has been proposed in which only one segment driver is provided to be shared by both the screens (thereby enhancing the duty ratio).
Meanwhile, the interface of the above-mentioned (high duty ratio) liquid crystal display apparatus is different from the interface used on the preceding dual-scan liquid crystal display apparatuses. Consequently, the preceding dual-scan liquid crystal display apparatus installed on a system cannot be directly replaced with the above-mentioned (high duty ratio) liquid crystal display apparatus.
Further, the above-mentioned (high duty ratio) liquid crystal display apparatus presents a problem of lowered display quality caused by decreased contrast and increased crosstalk.
In order to solve these problems, a liquid crystal display apparatus as disclosed in Japanese Published Unexamined Patent Application No. Hei 9-22275 for example has been developed. In the disclosed liquid crystal display apparatus, m types of orthogonal functions and, in each of the upper and lower screens, m/2 common electrodes are simultaneously selected, and a signal based on the orthogonal functions is applied to the selected common electrodes.
In this case, however, a difference between the drive frequency of the common electrode on the upper screen and the one on the lower screen is conspicuous, thereby lowering display quality.